Because LCDs have the advantages of portability, low power consumption, and low radiation, they have been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras, and the like. Furthermore, LCDs are considered by many to have the potential to completely replace CRT (cathode ray tube) monitors and televisions.
FIG. 2 is essentially an abbreviated circuit diagram of a typical LCD 10. The LCD 10 includes a first substrate (not shown), a second substrate (not shown) facing the first substrate, a liquid crystal layer (not shown) sandwiched between the first substrate and the second substrate, a gate driver 11, a data driver 12.
The first substrate includes a number n (where n is a natural number) of gate lines 13 that are parallel to each other and that each extend along a first direction, and a number k (where k is also a natural number) of data lines 14 that are parallel to each other and that each extend along a second direction orthogonal to the first direction. The smallest rectangular area formed by any two adjacent gate lines 13 together with any two adjacent data lines 14 defines a pixel unit (not labeled) thereat. The first substrate also includes a plurality of thin film transistors (TFTs) 15 provided in the vicinity of the intersections of the gate lines 13 and the data lines 14. The first substrate further includes a plurality of pixel electrodes 151 formed on a surface thereof facing the second substrate. The second substrate includes a plurality of common electrodes 152 opposite to the pixel electrodes 151.
In each pixel unit, a gate electrode of the TFT 15 is connected to the corresponding gate line 13, a source electrode of the TFT 15 is connected to the corresponding data line 14, and a drain electrode of the TFT 15 is connected to a corresponding pixel electrode 151. In each pixel unit, the pixel electrode 151, the common electrode 152 and the liquid crystal layer sandwiched therebetween define a capacitor 153.
The gate driver 11 is connected to the gate lines 13 for providing a number of scanning signals to the gate lines 13. The data driver 12 is connected to the data lines 14 for providing a number of gradation voltages to the data lines 14.
FIG. 3 is an abbreviated waveform diagram of driving signals of the LCD 10. The scanning signals G1-Gn are generated by the gate driver 11, and are applied to the gate lines 13. The gradation voltages (Vd) are generated by the data driver 12, and are sequentially applied to the data lines 14. A common voltage Vcom is applied to all the common electrodes 152. Only one scanning signal pulse, e.g., a scanning pulse 19, is applied to each gate line 13 during each single scan. The scanning pulses 19 are output sequentially to the gate lines 13.
In a first frame, the gate driver 11 sequentially provides the scanning pulses 19 (G1 to Gn) to the gate lines 13, and activates the TFTs 15 connected to the gate lines 13. When the gate lines 13 are scanned, the data driver 12 outputs gradation voltages Vd corresponding to image data PD to the data lines 14. Then the gradation voltages Vd are applied to the pixel electrodes 151 via the activated TFTs 15. The potentials of all the common electrodes 152 are set at a uniform potential. The gradation voltages Vd written to the pixel electrodes 151 are used to control the amount of light transmission at the corresponding pixel units and consequently provide an image displayed on the LCD 10. In a second frame, gradation voltages Vd′ corresponding to image data PD′ are applied to the pixel electrodes 151 via the activated TFTs 15 when the gate lines 13 are scanned by scanning pulses 19′.
In FIG. 3, the gradation voltages Vd are signals whose strength varies in accordance with each piece of image data, whereas the common voltage Vcom has a constant value and does not vary at all.
If motion picture display is conducted on the LCD 10, problems of poor image quality may occur for a variety of reasons. For example, a residual image phenomenon may occur because a response speed of the liquid crystal molecules is too slow. In particular, when a gradation voltage variation occurs, the liquid crystal molecules are unable to track the gradation voltage variation within a single frame period, and instead produce a cumulative response during several frame periods.
It is desired to provide an LCD and a method for driving an LCD which can overcome the above-described deficiencies.